Elimination of river blindness feasible: WHO study shows that areas in Mali and Senegal require no further mass treatment

TDR press release
21 July 2009

21 July 2009: The first evidence that onchocerciasis elimination is feasible with ivermectin treatment was published today in the open-access journal PLoS Neglected Tropical Diseases. Onchocerciasis is also called river blindness because the blackfly which transmits the disease breeds in rivers; it often blinds people, as well as causing debilitating skin disease. Over 37 million people are infected, often living in poor, rural African communities.

"This evidence is an historic milestone -- it has far-reaching implications for the fight against this disease. Prior to this study we did not know if we would ever be able to stop treatment," says Uche Amazigo, the Director of the African Programme for Onchocerciasis Control (APOC). APOC is the organization charged with implementing control of the disease across Africa.

The multi-country study showed that treatment with ivermectin stopped further infections and transmission in 3 specific areas in Africa where the disease has existed continuously (an endemic area).

Ivermectin kills the larvae but not the adult worms of Onchocerca volvulus, the parasite that causes the disease, so annual or biannual treatments are required to prevent resurgence. Merck & Co., Inc., the company that discovered and manufactures the drug, agreed in 1987 to donate the drug free of charge to countries where onchocerciasis is endemic. This has resulted in annual treatments to all eligible community members – over 60 million people were treated in 26 African countries in 2008. But although this large scale treatment has enabled the control of onchocerciasis in Africa, it has not been clear whether it could also be used to eliminate infection and transmission to the extent that treatment with ivermectin could be safely stopped. Many scientists have doubted whether onchocerciasis elimination with ivermectin is feasible in Africa, where more than 99% of cases are found.

This new study in three areas in Mali and Senegal where onchocerciasis was endemic has now provided the first evidence of the feasibility of onchocerciasis elimination with ivermectin in some endemic areas in Africa. Previously it was thought that elimination of onchocerciasis was only possible in the limited, isolated areas in the Americas where the disease is endemic. However, the studies showed that after 15 to 17 years of six monthly or annual treatments, only a few infections remained in the human population. Transmission levels were below predicted thresholds for elimination, so treatment was subsequently stopped in test areas and follow-up evaluations after 1.5 to 2 years showed that no further infections or transmission occurred.

Although further studies are needed to determine to what extent these findings can be extrapolated to other areas in Africa, the principle of onchocerciasis elimination with ivermectin treatment has been established. Dr Robert Ridley, Director of TDR, the Special Programme for Research and Training in Tropical Diseases (that coordinated the study), said, "This is an excellent example of how research like this can not only provide important answers to major health questions, but with this type of partnership, can also help develop research capacity in low income countries."

As a result of the study, the board of APOC has already adopted a new objective for the program to determine where and when treatment can be safely stopped in the 16 African countries where APOC is supporting mass ivermectin treatment programs.

The studies were undertaken by research teams from the ministries of health of Mali and Senegal, in collaboration with the WHO Multi-Disease Surveillance Centre in Burkina Faso. Main funding for the study was provided by the Bill & Melinda Gates Foundation. The study was coordinated by TDR, the Special Programme for Research and Training in Tropical Diseases, a co-sponsored programme of UNICEF, UNDP, the World Bank and the World Health Organization (WHO). TDR conducted much of the earlier research to prove that this drug was safe and effective. The partnership with Merck & Co., Inc., the MECTIZAN Donation Program, WHO, APOC and the national control programmes is considered an early model of the numerous public-private partnerships that have sprung up in the last decade.

Contact information

Jamie Guth
TDR Communications Manager
Telephone: + 41 79 441 2289
E-mail: guthj@who.int

Dr Hans Remme
Overall study coordination
Telephone: + 33 64 5457 404
E-mail: hansremme@gmail.com

Dr Mamadou Oumar Traore
Principal investigator
Mali study team
Telephone: +223 66 71 17 66
E-mail: traoremot@yahoo.fr

Dr Lamine Diawara
Principal investigator
Senegal study team
Telephone: +221 76 683 03 18
E-mail: elddiawara@gmail.com

Dr Yiriba Bissan
Senior Entomologist
Multi Disease Surveillance Centre (MDSC), Ouagadougou
Telephone1: + 226 71 08 30 94
Telephone2: + 226 75 59 56 64
E-mail: yiribab@yahoo.fr